The inherited helm of Ares is Darrow's proof of connection to the old rebellion and the token he plans to carry to Athena's Daughters at Kalyke.
The Helm of Ares is the emblem Darrow intends to present when he answers Athena's invitation at Kalyke. In the current crisis its practical value is political rather than martial: it identifies a claimant to the legacy of the Sons of Ares before the hidden Daughters of Ares who may have every reason to treat Darrow as an enemy.
The helmet carries the burden of that legacy because Darrow once gave House Raa the names of Rim Sons of Ares in exchange for Romulus's help against Roque. The resulting purge killed the people whose memory the helm invokes. Taking it to Athena is therefore not a claim of uncomplicated authority, but an admission that the old rebellion's symbols belong also to those Darrow failed.
If Athena accepts the token and Darrow's accounting, the helm may open the way to the Daughters' hidden ships and a renewed chance to reinforce Mars. If she rejects him, it will mark the distance between inheriting Ares's cause and deserving it.
The helm is not newly described in this chapter. It is known as the distinctive inherited headpiece and symbolic regalia of Ares.
The Helm of Ares is Darrow's credential and confession as he seeks an audience with the Daughters rather than a weapon that can compel their loyalty.